CMOS image sensors can be integrated with all kinds of functional circuitry and blocks in a single chip. A digital imager typically can include a photodiode array, column readout structure, A/D conversion, and digital controllers (or processors) on single or multiple substrates. In a conventional front-side illuminated (FSI) imager, incident photons first cross metal connection layers before reaching the photodiodes, causing a portion of the incident photons to be reflected away from the photodiodes. Conventional back-side illuminated (BSI) imager can divide the photodiode and circuitry into different strata, providing photons to the photodiodes directly from the other side of the substrate.
FIG. 1 depicts conventional four-side buttable BSI imager 100 using multiple layers of chips stacked in a three-dimensional (3D) package. On a first layer, the 3D BSI imager includes imaging sensor array 110 with pixels containing photodiodes that are exposed to incident light. Traces 120 route the pixel output(s) to layers of silicon stack 130. The silicon stack can include top and bottom aluminum nitride substrates 132, 133. Between the AIN caps can be rerouting interposer 134 along with analog-digital converter (ADC) master control chip 136 and ADC slave control chip 137. System interface 140 can be connected to BSI imager 100 via spring-loaded (POGO) pins 145.